Yes I would guess it is that way for a good reason. I did not like having an option that says "Clear Value" that would not work as expected, so I had two options:
- Correct the behavior to match what the option says. That is the option I went for.
- Remove or disable that option (only for standard date columns)
I figured that since Calibre allows removing standard date using the bulk metadata editor, it should not be a problem to offer the same option in the plugin.